The inlet cofferdam of the expansion engineering of Wuqiangxi hydropower station consists of the reserved rock barrier, concrete, soil and stones. The rock barrier is a bedding slope with relatively developed soft interlayers, which results in a complicated geological condition and blasting demolition environment for the cofferdam. In the process of demolishing the bedding rock barrier, it is impossible to break the rock once in a large area according to the economic section of a conventional cofferdam due to the large engineering quantity of the underwater blasting excavation, high requirement of fragmentation, long construction time and high risk. Under the condition of ensuring the stability of the cofferdam, the method of vertical stratification, horizontal zoning and loosening bench blasting was adopted to implement land excavation as much as possible. For the underwater blasting, according to the geological conditions of rock barrier, the mechanical characteristics of rock mass, the water depth (20~37 m) and the fragmentation requirement, the powder factor of 0.9~1.1 kg/m³ and maximum charge per delay of 60 kg was adopted. Electronic detonators were used for blast hole initiation and a series of safety measures such as bubble curtains and flexible protective nets were set. The field monitoring results show that the effect of blasting vibration and water percussive wave on structures such as inlet gate has been effectively controlled, and the efficiency of underwater slag removal and transfer has been improved.